Insulated conductor



June 4, 1935. GRAY 2,003,772

INSULATED CONDUCTOR Filed Dec. 16, 1930 INVENTOR AN. GRAY v A TTOPNEY Patented June 4, 1-935 UNITED STATES PATENT OFFICE INSULATED CONDUCTOR Alvin N. Gray, Baltimore, Md., assignor to Bell Telephone Laboratories,

Incorporated, New

York, N. Y., a corporation of New York ApplicationDecember 16,.1930, Serial No. 502,667

9 Claims.

be extremely flexible to permit frequent bending and twisting without impairing the transmission characteristics of the set. To obtain this flexibility such conductors aremade up of a number of very fine conducting wires or strips suitably grouped together. Furthermore, when such conductors are to be employed in damp places it is the usual practice to protect such conductors against corrosion by applying a protective coating of vulcanized rubber insulation. In applying' this layer of rubber it is the present practice to bring about vulcanization with the aid of sulphur and an accelerating agent. In the case of ordinary conductors wherein the cross-section of the conducting wires or strips that go to make up the conductor is relatively large this processv is fairly satisfactory. However, in cases where this cross-section of the conducting wires or strips is relatively small, for example, in the case of tinsel cord conductors, this process is very unsatisfactorysincein such cases the free sulphur which is ordinarily liberated in time corrodes the conducting wires or strips to a point where they are unsatisfactory for service or even where they are completely destroyed thus defeating the purpose for which the layer of rubber insulation was primarily applied.

The object, therefore, of the present invention is to produce an insulated conductor comprising one or more fine conducting wires or strips, the transmission characteristics of which remain substantially constant.

In accordance with the present invention this object is attained by coating-the conductor with a layer of rubber composition and then vulcanizing this composition with the aid of such agents that the amount of sulphur which remains uncombined is reduced to a minimum. In accordance with the preferred process the rubber composition is vulcanized with the aid of sulphur and an organic accelerator such as tetramethylthiuramdisulfide or as it is generally called Tuads. This Tuads however contains a certain percentage of sulphur which is liberated during the vulcanizing process and it has been found that the sulphur thus liberated when combined with the sulphur ordinarily added produces an excess of sulphur which remains uncombined and is available therefore as a corrosive agent. By properly proportioning the amount of sulphur which is ordinarily added and the amount of sulphur in the accelerating agent it is possible to make available just the amount of sulphur needed to produce a satisfactory vulcanization without leaving uncombined sulphur in the composition.

In accordance with a modification of this process the rubber composition is vulcanized with the aid of Tuads alone. In this modification a sufiicient amount of Tuads is added to the mixture so that the sulphur which is liberated is sufficientto produce satisfactory vulcanization without leaving uncombined sulphur in the composition.

The use of such compounds, that is sulphur and Tuads, is old in the art of vulcanizing rubber having been used heretofore to increase the speed of vulcanization but as far as applicant is aware no one prior to applicants invention has conceived the idea of properly proportioning the amount of the vulcanizing agents to prevent corrosion on fine conducting wires caused by a certain percentage of the added sulphur remaining uncombined in the rubber compound.

A clearer understanding of this invention may be had by reference to the accompanying drawing which shows a conductor insulated in accordance with the present invention.

As shown by the drawing a tinsel cord conductor is madeup of a number of individual conductors, each individual conductor comprising a very fine conducting wire or strip l0 helically wrapped around a strand of textile material II. The conductors thus formed are then preferably twisted about a core of textile material l3 to obtain the necessary mechanical strength and are then bound together by two servings i4 and I5 of textile material which are wound about the conductor in opposite directicns. When these conductors are to be employed in damp places they'are protected against corrosion by applying a protective coating of vulcanized rubber insulation I6. Two such conductors are usually grouped together and held in place by an outer braiding of textile material ll. In accordance with the present practice the layer of rubber is applied by extruding a mass of rubber containing sulphur and an accelerating agent about the conductor and then applying heat. During the heating the sulphur,

under the influence of the accelerating agent,

combines with the rubber and thus brings about vulcanization. During this process however it has been found that a certain amount of the sulphur remains free or uncombined and. is therefore present as a corrosive agent. In the case of the ordinary conductor the corrosive action produced bythe uncombined sulphur is relatively unimportant but it becomes of vital importance in the case of the tinsel cord conductors wherein the thickness of individual conducting strips is in the neighborhood of approximately 1 mil since in such cases the corrosion soon renders the conductors unsatisfactory and in some cases may. completely destroy the conductor thus defeating the purpose for which the layer of rubber insulation was primarily employed.

In accordance with the preferred form of the present invention this corrosive action is avoided by vulcanizing the layer of rubber composition with the aid of sulphur and an organic accelerator such as tetramethylthiuramdisulfide or, as it is generallycalled 'Iuads, the percentages of the sulphur and "Tuads used being such that no uncombined sulphur remains in the compound after'vulcanization. While the following formula is preferred yet it is to be understood thatit is given merely for the purpose of illustration and that the various elements and the percentages thereof maybe varied as occasion demands:

Pale crepe rubber 32.0 Reclaimed white rubber 20.0 Tetramethylthiuramdisulfide 1.0 Sulphur 0.3 Zinc oxide 3.0 Neozone 1.0 Stearic acid 0.2

Di-phenyl-g'uanidine 0.5 Whiting 42.0

After the above composition has been thoroughly mixed a coating of a predetermined thickness is extruded about-a'conductor in any suitable manner. The conductor thus coated is then covered with talc and placed in a vulcanizer where it is heated for approximately 20 minutes to about 275 F. During this heating process the sulphur combines with the rubber and brings about vulcanization, the rate of vulcanization depending to agreat extent upon the amount of accelerant used. Inasmuch as the Tuads contains a certain percentage of sulphur which is freed during the heating, it is necessary to carefully proportion the amount of sulphur and the amount of 'Iuads, otherwise there will be a certain percentage of sulphur which will remain uncombined and thus corrode the very fine conducting strips.

While the foregoing is the preferred method of vulcanizing the rubber omposition yet good results'may be obtained by the use of Tuads alone. In this case the percentage of the 'Iuads is increased to the point where the sulphur which is freed during the heating of the Tuads" is just sufficient to produce a thorough vulcanization without leaving any uncombined sulphur. What is claimed is: I

1 The method of preventing corrosion of conductors which consists in coating said conductors with a rubber compound and vulcanizing said compound with the aid of sulphur and an organic accelerator containing sulphur, said organic accelerator being'ad ded in suflicient quantities to bring the sulphur content of the mixture -to the predetermined value required to cause the vulcanizing action to go to completion with the elimination of I free sulphur in the resulting vulcanized rubber.

5 The method of preventing corrosion of conduc ors which consists in coating said conductors with a rubber compound and vulcanizing said compound with the aid of sulphur and tetramethylthiuramdisulfide which are added to the rubber compound in such quantities as to bring the total sulphur content to the predetermined value necessary to carry the vulcanization reaction to completion without leaving any uncombined sulphur in the vulcanized product.

3. The method of preventing corrosion of conductors which consists in coating said conductors with a rubber compound containing a known percentage of sulphur and vulcanizing said compound with the aid of tetramethylthiuramdisulfide which is limited in amount so that the sulphur released from it during the vulcanization process together with that contained in said bber compound will be just suflicient to carry the reaction to completion without leaving uncombined sulphur in the resulting insulating layer.

4. The method of insulating an electrical conductor which comprises extruding a rubber composition containing at .least one per cent of tetramethylthiuramdisulfide and substantially three tenths of one per cent sulphur and vulganitzing said composition under the influence of 5. The method of preventing corrosion of conductors which consists in coating said conductors with a rubber composition containing a known percentage of sulphur, vulcanizing said composition with the aid of sulphur containing accelerating agents such as tetramethylthiuramdisulfide and a non-sulphur containing accelerating agent such as diphenylguanidine, said tetramethylthiuramdisulfide lieing quantitatively added to increase the sulphur content of the mixture to an amount required to cause the reaction to go only to completion, without leaving any uncombined sulphur in the vulcanized product.

6. The method of preventing corrosion of conductors which consists in coating said conductors with a rubber composition containing a known percentage of sulphur, vulcanizing said composition with, the aid of a tetraalkylated thiuramdisulflde and a disubstituted guanidine, said thiuramdisulfide being added to increase the sulphur content of the mixture to an amount required to cause the reaction to go only to completion without leaving any uncombined sulphur in the vulcanized product.

7. An electrical conductor comprising a conducting core and a layer of vulcanized insulation thereupon containing before vulcanization approximately 1 part of tetramethylthiuramdisulphide and 0.3 parts of sulphur to 39 parts of rubber.

8. An electrical conductor comprising a conducting core and a layer 01' vulcanized insulation thereupon, free from uncombined sulphur, said insulation containing before vulcanization free sulphur, a sulphur containing accelerant and a non sulphur containing accelerant'.

9 An electrical conductor, comprising a conducting core and a layer of vulcanized rubber.

compound thereon, which rubber compound contained before vulcanization free sulphur and a sulphur containing organic accelerant in such proportions that upon vulcanization the com- 

